A global navigation satellite system (GNSS) is a satellite navigation system with global coverage and comprises the global positioning system (GPS), the Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS), the BeiDou navigation satellite system, Galileo, the independent regional navigation satellite system (IRNSS), and the quasi-zenith satellite system (QZSS). The GNSS is typically used for navigation on land, sea, and air. A vehicle, for example, an aircraft, a helicopter, a ship, a truck, etc., may have a navigation sensor with an inbuilt GNSS receiver on board with a standard GNSS antenna and cable assembly. The GNSS receiver comprises a radio frequency port that connects the GNSS receiver to the GNSS antenna via the cable assembly. The GNSS receiver processes GNSS signals transmitted by satellites, and determines position and velocity of the vehicle, and precise time. The GNSS signals transmitted by the satellites are weak radio frequency (RF) signals. Since the satellites are in motion, the GNSS receivers have to continuously acquire and track the transmitted GNSS signals from the satellites in view. The GNSS antenna captures the transmitted GNSS signals.
Global navigation satellite system (GNSS) antennas are of two types, namely, a passive GNSS antenna and an active GNSS antenna. The passive GNSS antenna has no amplification stages. The active GNSS antenna is an antenna with an integrated signal amplifier. The active GNSS antenna is used for receiving GNSS signals. The integrated signal amplifier boosts a GNSS signal picked up by the active GNSS antenna and allows for a longer remote cable run between the GNSS receiver and the active GNSS antenna. The cable between the GNSS receiver and the active GNSS antenna is a coaxial cable. On transmission of the received GNSS signal by the active GNSS antenna, the GNSS signal is attenuated throughout the length of the cable. The longer the cable, the larger is the loss in the strength of the transmitted GNSS signal. The integrated signal amplifier compensates for the loss of the GNSS signal strength by boosting the captured GNSS signal before transmitting the GNSS signal to the GNSS receiver.
In certain situations, a user of the global navigation satellite system (GNSS) receiver may need to upgrade performance of the navigation sensor of the vehicle by adding an additional GNSS receiver with improved capabilities to the existing GNSS receiver. Addition of the additional GNSS receiver requires an installer to drill holes on a vehicle surface to install an additional GNSS antenna, which significantly increases the cost of installation. Moreover, addition of the additional GNSS receiver requires adding long cable assemblies from the additional GNSS antenna to the additional GNSS receiver. As the number of parts of the active GNSS antennas, that is, the existing GNSS antenna and the additional GNSS antenna, installed on the vehicle increases, complexity in assembly of the parts of the GNSS antennas increases and results in additional weight of the setup of the additional GNSS antenna and significant costs for installation of the additional GNSS antenna. Long coaxial cable runs between the additional GNSS antenna and the additional GNSS receiver further increase the costs. Hence, there is a need for sharing the existing GNSS antenna by the existing GNSS receiver and the additional GNSS receiver to reduce the significant costs of installation and to avoid complexity of the setup created by long coaxial cable runs.
In a conventional system where a global navigation satellite system (GNSS) antenna is shared between two GNSS receivers, a radio frequency (RF) splitter is connected between the two GNSS receivers for splitting the received GNSS signal into two GNSS signals and feeding one GNSS signal each to the two GNSS receivers. Insertion of the RF splitter in a cable run between the GNSS receivers results in insertion losses and also division of power of the received GNSS signal. In the RF splitter, approximately 3 decibel (dB) loss of power of the GNSS signal received by the GNSS antenna is observed at each of the output ports of the RF splitter, thereby attenuating the split GNSS signal significantly. There is a need for splitting the received GNSS signal into multiple GNSS signals with minimal attenuation.
The active global navigation satellite system (GNSS) antenna needs power to operate. The GNSS receiver powers the GNSS antenna via a connecting coaxial cable. In a conventional system where the GNSS antenna is shared by two GNSS receivers using the radio frequency (RF) splitter, the power to the GNSS antenna is provided by the GNSS receiver that is connected to the GNSS antenna via a cable assembly. Consider an example where a first GNSS receiver and a second GNSS receiver share a GNSS antenna and the power to the GNSS antenna is supplied by the first GNSS receiver. The RF splitter is connected between the first GNSS receiver and the second GNSS receiver. If the first GNSS receiver that was supplying power to the GNSS antenna is switched off or disconnected from a power source, the GNSS antenna will not be powered any longer. The second GNSS receiver that is connected to the RF splitter, in turn, stops receiving the GNSS signal and stops tracking the satellites until power to the GNSS antenna is restored. There is a need for a method and a system for supplying power to the shared GNSS antenna by either one of the GNSS receivers based on availability of the GNSS receivers, where the GNSS receivers are powered independent of each other and therefore ensure uninterrupted power supply to the shared GNSS antenna when either of the GNSS receivers is powered off.
A global navigation satellite system (GNSS) antenna typically requires a direct current (DC) voltage of, for example, about 4 volts (V) to about 18 V to receive and transmit a GNSS signal to the first GNSS receiver. Consider an example where the power to the GNSS antenna is supplied by the second GNSS receiver. The DC voltage from the second GNSS receiver has to be passed to the GNSS antenna to indicate any fault in the GNSS antenna to the second GNSS receiver. The second GNSS receiver is connected to the GNSS antenna via the first GNSS receiver using a long cable. That is, DC voltage from the second GNSS receiver will have to pass through additional circuitry in the first GNSS receiver on the path to the GNSS antenna. Ohmic losses in the additional circuitry will introduce an additional voltage drop in the DC voltage. Ohmic losses along the long cable that connects the second GNSS receiver to the GNSS antenna also reduce the voltage supplied to the GNSS antenna. There is a significant voltage drop throughout the long cable. The minimum operating DC voltage of an airborne GNSS antenna is, for example, about 4.4 V and the GNSS receivers typically supply a DC voltage of 5 V. Thus, any voltage drop in the path to the GNSS antenna from the second GNSS receiver can reduce the margin of DC voltage required to operate the GNSS antenna. Due to the voltage drop, the voltage at the input of the GNSS antenna is reduced and the GNSS antenna ceases to perform the intended function of receiving and transmitting the GNSS signal to the first GNSS receiver. Therefore, there is a need for minimizing the attenuation of the DC voltage supplied to the GNSS antenna over the additional circuitry in the first GNSS receiver and the long cable to less than 0.35 V, when the GNSS antenna is shared between GNSS receivers.
In each global navigation satellite system (GNSS), errors are inherent. The GNSS receivers must compensate for the errors to provide a reliable output. If the errors are not corrected, the GNSS receivers may provide poor performance and unreliable output. The sources of errors in the GNSS comprise, for example, the positioning and clock of the satellites, navigation messages transmitted by each satellite, faults in the GNSS antenna, faults in the long run of the cables, noise in the design of the GNSS receivers, etc. Typically, a controller on the GNSS receiver detects a fault in the GNSS antenna or a fault in the long cables run between the GNSS receiver and the GNSS antenna by monitoring current drawn by the GNSS antenna or a voltage drop along the long cables. The controller alerts a user of the GNSS receiver of an occurrence of any such fault. In systems where the GNSS antenna is shared between two GNSS receivers, for example, a first GNSS receiver and a second GNSS receiver, the second GNSS receiver is not directly connected to the GNSS antenna. The second GNSS receiver is unaware of the fault in the GNSS antenna or the long cable between the GNSS antenna and the first GNSS receiver. Therefore, there is a need for a method and a system for detecting and indicating an occurrence of a fault in the GNSS antenna or the long cable run between the GNSS antenna and the first GNSS receiver to the second GNSS receiver, when the GNSS antenna is shared between the first GNSS receiver and the second GNSS receiver.
Hence, there is a long felt need for a global navigation satellite system (GNSS) antenna sharing receiver and a method for sharing a single GNSS antenna on a vehicle with more than one GNSS receiver without affecting an existing antenna and cable assembly in the vehicle. Moreover, there is a need for a GNSS antenna sharing receiver and a method for splitting the received GNSS signal between the GNSS receivers with minimal attenuation. Furthermore, there is a need for a GNSS antenna sharing receiver and a method for minimizing the attenuation of direct current (DC) voltage supplied to the GNSS antenna to less than 0.35V, when the GNSS antenna is shared between multiple GNSS receivers. Furthermore, there is a need for a method for supplying power to the GNSS antenna based on availability of the GNSS antenna sharing receiver and the GNSS receivers, where the GNSS antenna sharing receiver and the GNSS receivers are powered independent of each other. Furthermore, there is a need for a GNSS antenna sharing receiver and a method for detecting and indicating an occurrence of a fault in the GNSS antenna or the long cable run between the GNSS antenna and the GNSS receivers.